Influenza vaccine safety in pregnancy: can we identify exposures?

To assess the feasibility of identifying influenza vaccine exposure in pregnancy.

Two study designs were used. (i) Women who contacted the Organization of Teratology Information Specialists (OTIS) network and were referred to their research center or contacted the center directly were invited to participate. (ii) Vaccine exposure information was gathered within an ongoing case-control surveillance program, the Slone Birth Defects Study (BDS). To confirm vaccine exposure and obtain details (e.g., brand name, presence of thimerosal), we requested medical records. If records were not available, we contacted the provider for information regarding the vaccine product used in that setting. If the provider used only one vaccine product during the reported exposure period, we assumed those vaccine details applied to the reported exposure. Otherwise, no details could be inferred.

Between September 2006 and February 2008, OTIS enrolled 106 women who reported influenza vaccine exposure during pregnancy. Vaccine was confirmed for 100 (94.3%); brand was confirmed for 87 (82.1%). Among 2177 BDS interviews completed during the same period, 462 (20.8%) reported influenza vaccine exposure; brand and formulation were available for 314 (69.5%). Over one quarter of the BDS women (29%) received their vaccine in nontraditional settings, where influenza vaccine exposure would not likely be recorded in their medical record.

We demonstrated the capacity both to identify influenza vaccine exposure in pregnancy and to obtain important details of the specific vaccine administered. Many women receive influenza vaccines outside of typical health care settings, which has important implications for influenza vaccine studies that rely on medical records.